COURTAULDS LYOCELL™ FOR TECHNICAL TEXTILES

Calvin R Woodings

INTRODUCTION

World production of man-made fibres has shown linear growth from 3.4 million tonnes in 1960 to 20 million tonnes in 1993. Over the same period, the main competitor, cotton, has grown from 10 to 20 million tonnes. In volume terms at least, man-made synthetics have been the most successful fibres of this generation, this success being due to their superior durability, their easy processing and care performance and the ready availability and low cost of fossil fuels.

Man-made cellulosics have not grown, sales being 2.6 million tonnes in both 1960 and 1993 despite peaking at 3.8 million tonnes in 1973. Their market share has fallen from 18% in 1960 (similar to the synthetics) to 7% in 1993 (compared with 50% for the synthetics) Synthetics have grown by offering progressively improved cost/performance benefits in textiles of all kinds.

Viscose staple, the leading man-made cellulosic fibre, has, of necessity, repositioned itself from the lowest cost commodity fibre of the 60’s and 70’s to a premium priced speciality fibre for the 90’s. Its current “niche” position was forced by its inability to make serious progress against cotton (price, aesthetics, image) while losing segment after segment to lower cost, more durable synthetics. While synthetics producers were able to drive down costs year after year, viscose producers had to spend significant capital just to stay ahead of environmental legislation. Those who either overspent or underspent were forced to close. In the shrinking market the survivors, unable to finance much needed modernisation schemes, faced extinction.

Courtaulds chose to try to avoid this trap by developing a new environmentally benign cellulose processing-route. The “Genesis” project of the 80’s became the “Tencel” business of the early 90’s, as the new fibre was launched into fashion apparel segment commencing in Japan where sophisticated finishing techniques allowed unusual garment aesthetics to be developed. The Japanese demand for these aesthetics allowed rapid growth, and fashion apparel became an attractive launch segment which has since been replicated in the US and Europe.

PROCESS EVOLUTION

The increasing importance of reducing the environmental impact of the viscose process coupled with the increasing likelihood that the newer cellulose solvents would be capable of yielding a commercially viable fibre process led Courtaulds to embark on a systematic search for a new cellulosic fibre process in the late 1970’s.

By 1980, NMMO was shown to be the best solvent provided well-known difficulties associated with its thermal stability could be avoided by appropriate chemical engineering. Filaments obtained from the first single-hole extrusion experiments had promising properties so Courtaulds committed the resources in 1982 to build the first small pilot plant to test the feasibility of overcoming the solvent handling and recovery problems which had prevented earlier commercial exploitation. This system, capable of making up to 100 kg/week of fibre, met its objectives and allowed the first serious end-use development to begin. Scale-up to a 1 tonne/week pilot line was possible in 1984, and in 1988 a 1000 tonne/year semi-commercial line was commissioned to allow a thorough test of the engineering and end-use development aspects.

Continuous operation of this semi-commercial line provided the necessary confidence in both process and market to justify commercial operation. The first full plant (18,000 tonne/year in total) was therefore designed and built in Mobile Alabama in 1991/92. This plant has been supplying fibre to major apparel markets worldwide for the last 4 years and has proved the viability of the process and identified large potential markets for the new fibre. In early 1996 a further fibre plant was commissioned, also in Mobile, and this has increased the capacity to 43,000 tonnes/year. At the same time, construction of the first European factory commenced at Grimsby in the UK, with the intention of bringing Courtaulds capacity for the fibre to around 100,000 tonnes/year by the end of 1997. A third production site is now being sought in the Far East.

This rapid expansion will enable not only deeper penetration of apparel markets but also the development of modified versions of the fibre specifically for technical applications. So, while the main thrust of commercialisation remains with the fashion-oriented yarns and fabrics branded TENCEL®, the commercialisation of technical applications for the fibre, Courtaulds Lyocell™ , commenced at TechTextil in June of 1995, and this development is the subject of this paper.

TECHNICAL USES

Fibre markets are divided into Apparel, Home Furnishings and Technical Uses by the International Committee for Rayon and Synthetic Fibres (CIRFS). Their annual statistics provide a guide to segmentation.

Table 1 provides their breakdown of staple fibre consumption in Europe in the Technical Uses sector by application in 1993.

Technical Uses can be seen to cover a wide range of finished products including “unspun” end-uses. In CIRFS statistics these are EDANA- definition nonwoven fabrics plus waddings, fillings, felts, flocks and stitch-bonded fabrics, but excluding polymer-to-fabric routes such as spun-laid and melt-blown.

The sector does however have some common characteristics which tend to differentiate it from the other sectors - especially apparel:

• • Fabric performance is more important than aesthetics
• • New product lead times tend to be long.
• • New fibres are judged on technical merit.
• • Changes of raw-material are not undertaken lightly.
• • Markets are less volatile than fashion markets.
• • Barriers to entry can be high, but so can barriers to exit.
• • They are driven by technological change, not fashion.

COURTAULDS LYOCELL™ ATTRIBUTES FOR TECHNICAL USES

The Fibre

Lyocell is made from a natural, renewable polymer (cellulose) by an environmentally friendly process (direct dissolution of pulp). Courtaulds version has a highly crystalline molecular structure comprising bundles of fine fibrils which can be liberated in later processing if required. It has a circular section of 11-13 microns diameter at 1.7 dtex, and a saw-tooth mechanical crimp. It is easy to open and card and can be converted into nonwovens or spun-yarns of high uniformity. It is strong, especially when wet, has high wet and dry modulus and low extensibility. It is highly absorbent with a higher resistance to wet-collapse than viscose. The fibre does not shrink on wetting/drying, but the diameter swells reversibly by about 30%. Its chemistry is as for cellulose, but its DP and crystallinity confer better alkali, bleach, enzyme and heat stability than other cellulosics. It is easy to blend with other fibres.

In addition to the obvious spun and unspun applications for such a fibre, its ability to fibrillate and create micro-fibres in wet-processing allows its use in special papermaking systems, and in the reinforcement of woodpulps intended for use in absorbent products. If the micro-fibres are obtained dry, their high modulus and excellent adhesion to resins, polymers and latexes allows their use as reinforcing fibres for some structural composites and building materials in place of glass or other reinforcing fibres.

Spun Yarns

The fibre can be ring or rotor-spun into a wide range of yarn counts characterised by unusually high strength and cleanness. Fibre to yarn strength conversion efficiency is higher than for most other fibre types, the 42 cN/tex fibre typically giving 20 tex yarns with tenacities of around 28 cN/tex (ring-spun) or 20 cN/tex (rotor spun). These values are about twice those achievable with combed cotton. Properly constructed and finished multi-ply yarns make, for example, excellent cords, hose reinforcement, cable reinforcements, sewing threads and embroidery yarns.

Woven and Knitted Fabrics

The high strengths and moduli of the fibre translate into fabric properties characterised by high tensile and especially high tear resistance compared with cotton. Properly constructed and finished fabrics show excellent wash-stability, and an abrasion resistance comparable to cotton fabrics. The strength, non-melting, and low-creep characteristics of the fabrics offer the basis for many technical products for example, coating bases, abrasive substrates, printers blankets, rubber reinforcement, composites, flame- retardant cloths, belting, protective clothing, workwear, tenting, medical textiles.

Fibrillation of the fibre to micro-fibres after fabric construction has been widely successful in the apparel sector to create unique aesthetics (“peach-skin”). Similar techniques would be appropriate for technical textiles wherever the microfibres were required to confer, for instance, better breathable-barrier performance, suede-like surfaces, better filtration performance, or better adhesion to coatings or other materials.

Nonwoven Fabrics

The fibre converts into clean, uniform webs on all the main carding systems, on air-layers, wet-lay machines and on aerodynamic web formers. It can be bonded with latexes, with melting fibres or powders, by needling, stitching or hydroentangling.

On all the systems tested to date, the fibre strength appears to be converted into fabric strength, with values from 1.5 to 3 times those achieved with viscose being possible. When webs are wet processed, draw-down and shrinkage levels are lower than for viscose so the area yield can be as much as 15% higher. Achievable basis weight ranges are higher, the fibre being particularly good in hydroentanglement where the minimum achievable fabric weights can be 30% lower than possible with viscose. The high wet-cohesion of the fibre allows it to be wet-laid without other binder fibres, and if this cohesion is supplemented by some fibrillation, strong, all-cellulose nonwovens can be produced.

Nonwoven applications for the fibre include medical swabs and dressings, hygienic absorbents, wipes, coating bases, leather substitutes, filters, interlinings, diskette liners, battery separators, disposable and semi-durable apparel.

Special Papers

When refined, the fibres develop fibrils with a diameter of around 1 micron, although fibrillation of these fibrils can be also be observed. In special paper-making processes these fibrillated fibres can be formed into uniform sheets with several unusual characteristics which allow the development of many types of special filters, barrier sheets and membranes.

Fibre and fabric Disposal

Courtaulds Lyocell™ fibres biodegrade rapidly in composting or can be incinerated; the final breakdown products being carbon dioxide and water. These disposal methods simply recycle the cellulose to the atmospheric components from which it was made.

Some of the “free” solar energy which powered the manufacture of sugars and cellulose during photosynthesis may be reused through incineration or anaerobic digestion of the fibre. Slow anaerobic biodegradation occurs in all landfill sites dealing with municipal solid waste. This process generates methane from cellulose, which can be burnt to drive gas-turbines. Fast anaerobic digestion occurs in sewage treatment and the methane is burnt to power the sewage treatment process.

Courtaulds Lyocell™ fabrics can be shredded, pulped and recycled into paper or pulp-making processes.

CONCLUSION

In the last 5 years Courtaulds Fibres has proved that the production of fibre via the direct dissolution of woodpulp in a simple solvent has become a reality. The worldwide commercial success of the Tencel® branded fashion apparel fabrics and the scale up from a 1000 tonne/year pilot line in Grimsby to a 43,000 tonne/year factory in Mobile Alabama has removed any remaining doubts about the viability of this leading edge technology. The fibre is set to become a major new raw material for the world’s textile industries, and its extraordinary new-product potential will give textile technologists and fabric developers new opportunities well into the next century.

Calvin Woodings cw@nonwoven.co.uk

Please contact the author at the above address if you require copies of the slides used to illustrate this talk.

This paper was presented at the Textile Institute’s 77th World Conference, Tampere, Finland, May 23rd 1996.